1. The Field of the Invention
This invention relates to components for operation in ultra-pure environments and, more particularly, to novel systems and methods for providing long-lived pumps that are metal-free, ultra-pure, non-reactive, etc. for providing environments for hot, reactive or pure, liquids at elevated temperatures, with respect to ambient.
2. The Relevant Technology
Non-reactivity is a critical function in systems managing, transporting, or relying upon fluids. Fluids include gases and liquids. Many industrial processes rely on liquids, that may damage, weaken, leach, or otherwise interact with metals, elastomeric polymers, and other common materials.
One industry that has suffered with the limited technology available to provide high purity and temperature is the semiconductor processing industry. For example, hot, de-ionized water is used in numerous processes. Impurities are measured in parts per billion. Some materials may be hot acids used in etching and cleaning processes. Transporting, holding, heating, and other procedures for managing ultra-pure water, acids, and the like, are problematic in several ways.
For example, pumps have traditionally been made of metal. Metals are commonly used in the support structures of the pumps. Regardless of the xe2x80x9cstainlessnessxe2x80x9d of a metal, the purity requirements are not met by any known metals.
Polymers are often used for sealing members but may leach, react, degrade, or otherwise contaminate liquids. Moreover, polymers are typically not dimensionally stable. Polymers creep, stretch, yield, and otherwise become unreliable. Polymers (plastics, elastomers) respond to load, pressure, time, chemical environment, and, if any system failure occurs, may destroy any hope of reliability and xe2x80x9cfailing clean,xe2x80x9d failing to function yet leaving no contamination possible. Failures in the sealings may arise by creep or yielding of polymers. Leaks or other failures may expose materials during any failure. Accordingly, seals do not achieve perfect protection. The ability to avoid failures completely ranges from extremely difficult to impossible. Failures can be catastrophic if a system will not xe2x80x9cfail clean.xe2x80x9d
Contaminants in trace amounts which exceed allowable limits may destroy a batch of product. Physical destruction is not required. Rendering a silicon wafer, or other high purity substrate material, unusable due to contaminant reaction with a surface can waste product output. Down time for decontamination may be even more costly in actual lost production.
What is needed is a fluid handling system that is clean to extremely high standards. All materials that may potentially contact contained fluids, even in the event of failures, should be pure and non-reactive. Materials should tolerate temperatures in the range of 1 degree Celsius to 180 degrees Celsius. In some acids, temperatures may range from 100 degrees Celsius to 180 degrees Celsius.
Thus, stability over a broad range of temperatures, reliability in service, long life under exposure to extreme of temperatures, pressure, and reactive agents, and the like must all be tolerated. Repeatability of designs, and reliable repeatability over the lifetime of all installed apparatus in the system are very desirable. Currently, the most reliable pump mechanisms still depend on elastomeric seals and metal structural supports. Pumps do not have sufficient life and do not xe2x80x9cfail cleanxe2x80x9d in service. Upon failure, metals and elastomers are then exposed and are reactive. Thus, pumps still fail to maintain purity in failure or to operate reliably over many millions of cycles.
What is needed is a reliable, failclean, pump that operates over 10-50 million cycles, and that maintains purity, even in failure. Long term durability at elevated temperatures, pressures, and reactivities, without the threat of catastrophe at failure, is needed.
In view of the foregoing, it is a primary object of the present invention to provide a clean, high temperature, non-reactive, repeatable, producible, reproducible, low-cost, dimensionally stable, long-lived pump.
It is an object of the invention to provide a pump that will tolerate conventional manufacturing processes while providing suitable reliability and low-cost operation and maintenance for routine installations.
It is an object of the invention to provide a pump construction that can rely on readily available materials and readily available manufacturing processes at standard a manufacturing tolerances in order to maintain costs while providing reliability over tens of millions of cycles.
It is an object of the invention to provide reliable sealing in a pump, long-lived diaphragms at low cost, and a simple reliable mounting assembly that will support a fluid handling system and which will fail clean in the event of any failure.
Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an apparatus and method are disclosed, in suitable detail to enable one of ordinary skill in the art to make and use the invention. In certain embodiments an apparatus and method in accordance with the present invention may include a body and heads holding diaphragms with an associated adaptive seal. A union ring on each head may be provided, to connect to the body and to hold the diaphragm securely.
A pump may be assembled with threads. A union-type connector may hold the body and a head together. In one apparatus and method in accordance with the invention, a polymeric, preferably a fluoropolymer and non-reactive film, may form a diaphragm. The diaphragm maintains a single, substantially constant thickness without the need for changes in cross-section in order to accommodate mounting. The diaphragm may be contoured to fit a chamber so as to match the chamber wall at each end of a stroke. Accordingly, the diaphragm is fully supported when the pump is dead-headed, or backed up in a flooded or shut off position.
As a practical matter, no inflection point is required in the diaphragm during any unconstrained or unattatched point of its traverse. Hardware contact on the diaphragm is not substantial enough to cause overstressing, secondary creep, yielding or the like in the diaphragm.
The diaphragm is extremely reliable such that it becomes non-limiting in the life of the pump. Components close to the diaphragm use tight tolerances, closely matched angles, and short gaps between components. The configuration of the components provides for little unsupported material which reduces the stress within the material. No other loading is applied to the diaphragm. In the event of an air system failure, in an air-actuated pump, the high pressure applied to the diaphragm will be supported by the backing material on a chamber head or piston head. Likewise, since no buckling is required in the diaphragm, there is no change of direction and no inflection point within the chamber during operation. As a result, the life of the pump is greatly extended.
In one embodiment, the frame may be installed using a trapezoidal seal shim that produces a sharp angle bend, preferably less than or equal to 70 degrees. Thus, the diaphragms may be locked into trapezoidal slots, and held in place by trapezoidal shims, all comprising the same class of material, and preferably the exact chemically consistence or chemically identical material. Accordingly, the pump diaphragms limit any need for rim or compression seals, clamps, flanges, elastomeric seals, metals, and the like.
In one embodiment, the trapezoid may be irregular. One side may have a 70 degree angle, 20 degrees less than a right angle, and the other side may be a right angle. In another embodiment the trapezoid is regular and has a 70 degree angle, 20 degrees away from normal or perpendicular. The seal formed in a regular trapezoid becomes self centering.
The diaphragm is retained using no elastomeric materials, no rims, no metals, no flanges, no through-holes, and the like. Furthermore, the diaphragm is subjected to equalized loads. Prior art systems dealing with elastomeric materials will not fail clean. Moreover, creep is a factor in all fluoropolymers. However, geometries that can creep are adapted to conform to the seal, forming a tight mechanically adhesive load between the shim, the diaphragm, and the receiver slot for the shim.
A design after this mode prevents creation of diaphragm flange material that would pull in and increase diaphragm arc length. Increasing the diaphragm arc length tends to cause buckling or diaphragm roll at the point of flexure or the point of maximum flexure near the outer most confines of the chamber in which the diaphragm is located. Thus, even thin films of less than or equal to 30 thousands inch may be operated without buckling. Therefore, folding of the diaphragm and premature rupture of the diaphragm is avoided.
In one embodiment, a union nut is used to secure the head of the pump to the pump body or pump frame. A union nut is a slip ring having an aperture allowing the head to protrude there through away from the pump frame or pump body. The head may thus be registered, and the nut is fully free to slip circumferentially while loading the head longitudinally along the access of the driving rod between the pistons and diaphragms of the pump.
A non-reactive material, preferably a polypropylene is used to construct the entire nut. The nut applies a load to a cantilevered edge or lip of the head. Accordingly, primary creep is allowed to occur and loaded out. Thereafter, the head maintains sufficient spring properties, along with sufficient deflection under such spring properties, to maintain the minimum required loading of the head against the pump body at all times of service.
Moreover, the creep losses of thread materials and of the cantilevered head combine to permit less deflection than that required to maintain the spring loads in spite of continuing secondary creep. Therefore, head loading is maintained. The seal surface remains loaded and sealing. Pneumatic loading on the heads during actuation of the pump diaphragms is ineffective to cause excessive creep and unload the heads. Moreover, weeping, releasing chemicals, is eliminated. Moreover, compliant elastomeric seals are not required to act as energizers. Again, such a sealing system provides for a xe2x80x9cfail-cleanxe2x80x9d failure in the event of any potential failure.
In one embodiment, the heads of the pump may be provided with leak detectors. The leak detectors may be sealed away from the fluid of the pump by a window. The window is constructed of xe2x80x9cnon-reactivexe2x80x9d material that allows light to transmit.
In one embodiment, a thin diaphragm may be formed of polytetrafluoretheyne. In one embodiment, an anisotropic polymer is used. Moreover, in one embodiment, an expanded PTFE may be used.
Other plastics such as PFA may be used. Nevertheless, PTFE has been shown to be most effective. Moreover, by forming the diaphragm of PTFE, an amorphous fluoropolymer, a flexible diaphragm making a mechanically hermetic seal with the pump body and head (trapezoidal slot and shim) is so effective in practice that in certain circumstances minimal to no loading of the seal is required after a certain period of operational time.
Creep is ever present with fluoropolymers. Accordingly, threads creeping is typical when in tension and shrinking when in compression. Creep and shrinking presents a continuing problem in the use of fluorocarbons. In one embodiment, an entire pump may be assembled, with the lip on the edge of a head retained in an engagement portion of a slip ring or union nut threaded to the body of the pump.
Accordingly, creep will ensue in all components, the body, the cantilevered head portion and the slip ring or union nut. However, heat soaking and below ambient cooling under load may remove primary creep. Thereafter, the nut or union nut may be retightened on each end of the pump, maintaining dimensions within tolerances required for loading. Thus, secondary creep occurring after a heat soak and cooling cycle and loading of primary creep, is insufficient to unload the cantilevered member of the head, and thus maintains the head against the body in sealing relation.
A pump made in accordance with the invention improves operations substantially by including no metallic parts and no elastomeric parts. That is, an apparatus in accordance with the invention, is intended to xe2x80x9cfail clean.xe2x80x9d To fail clean signifies that a failure of any component within the pump, including any sealing component, results in no contamination of any liquids by reactive materials. Reactive materials include elastomeric polymers such as Neoprene(trademark), Viton(trademark), Nitrile, FKM, EPDM and the like. Other reactive materials include virtually all metals. Although some metals are considered non reactive, the requirements for the purity of liquids used in the semi-conductor processing industry is so strict that even xe2x80x9cnonreactivexe2x80x9d metals must be considered reactive in so far that the invention is concerned.
Thus, valves in the apparatus made in accordance with the invention contain no reactive components. Two types of strike valves or end-of-stroke valves are contemplated. In one embodiment, a short-stroke valve or poppet valve may operate at the end of a stroke of a diaphragm. The diaphragm, upon reaching the limits of the displacement permitted by a head portion of the operating cavity, contacts the head dome or cavity. Accordingly, a protrusion or post on a poppet valve is contacted by the diaphragm. The poppet valve opens a channel (air channel) to communicate with the now-evacuated head chamber over the diaphragm. The poppet valve, it""s actuator with a post integrally formed therewith, and a seat securable, such as threadable, to the head, may be provided.
In another embodiment, a long valve may be adapted to access the end of a stroke of a diaphragm or piston retreating away from the head and toward the body of a pump in accordance with the invention. A long-stroke, pilot valve may be designed to operate as a spool. Accordingly, a shank or shaft of the long-valve may be provided with a bumper maintained in contact with a diaphragm, such as against a diaphragm over an underlying piston head driving and being driven by the diaphragm.
The spool shaft, shank, tang, etc. thus extends into the chamber until the piston and diaphragm are halted by stops. Thereafter, chamber pressure may bleed through ports in the pilot valve to shift operation of the pump, by reversing the stroke. The spools may be designed as known in the art to use the main shaft, having a circumferentially extending channel, with cylindrical bearings passing over ports. Accordingly, bearings may selectively expose ports to circumferential channels, thus altering a position of the spool and subsequent channeling of flows between ports in a main housing surrounding the spool.
In one embodiment, only machined surfaces of nonreactive materials act as sealing surfaces. Additional wear may occur due to a lack of hardness, durability, abrasive-resistance, and the like. Nevertheless, nonreactive polymers maintain low core frictions with one another in certain embodiments. Moreover, any particulates from galling, wear, abrasion, fretting, and the like will nevertheless remain nonreactive. Accordingly, filters and traps within flow lines may typically remove such particulates, and the presence of such particulates will not cause leaching of contaminating ions into pumped fluids.
In one embodiment, no elastomeric seals are used in any valve, including principal check valves checking against back flows into the double chambers of the pump. Machined surfaces serve as sealing surfaces, and relief or clearance is provided in each circumstance where needed in order to maintain loads, tolerate secondary creep, following heat soaking primary creep out, such that loading and deflection requirements for sealing are maintained.
Metal springs are used in certain devices. Likewise, elastomeric seals, such as face seals or xe2x80x9cOxe2x80x9d rings and the like are often used in prior art systems to form seals. Downtime, lost processing batches, and the like are very expensive propositions. Accordingly, a fail clean system made in accordance with the invention relies on no metal springs, no metal washers, no metal retainers, and no metal of any kind. The fail clean system further does not rely on reactive, or organic materials exposed to operating fluids (gases, air) nor the transferred fluids (DI water, acids, hot acids, etc.). Any possible contact between the air chamber, or the liquid chamber in the pump (of which the pump has two of each, typically) eliminates all contact even in the air chamber with metals and elastomers.
In one embodiment of an apparatus and method in accordance with the invention, a base mounting system may be used for integrating a controller with a pump. Air controllers may be external and may be remote from a pump. However, mounting a pump is often problematic. Accordingly, a base is provided in which fluid conduits of the pump are formed to become the legs connecting a pump for mechanical support to a base. Meanwhile, the entire air controller mechanism may be formed in the base. Alternatively, the base may simply pass air through the pump from an external controller, depending on a users selection.
Several types of air control systems exist. A recirculating air system does not use high pressure. A high duty cycle is typical. Duty cycles bordering on 100 percent over many days may exist. Such a recirculating control system may operate non-stop indefinitely. An external control apparatus relies on a third party to connect a speed control to a pump installation. The third-party speed control dictates the amount of air flow to actuate a pump. Accordingly, reducing volume or pressure of incoming, driving air can be used to decrease the speed of operation of the pump. Thus, decreased displacement may be obtained directly by an external control.
A third type of control module may be a distribution unit. A distribution unit may operate under control of controlling mechanisms within the base. However, as a distribution unit, a pump in accordance with the invention may be dead-headed against a closed line. Thus, the entire pressure of the pump may be brought to bare against the pump and conduit system. A modular air pump may be made externally removable. However, a mount in accordance with the invention may be used for either recirculating air, external air vented to atmosphere after actuation of a cycle of the pump operation, or a distribution unit in which air is recirculated but the pump may be dead-headed against a closed line. A mount may provide a platform adapted to a universal pump. Adapted to different bases for control schemes.
By providing the opportunity for an external air system to mount to the base, the air logic transfer passages may be connected to the pump body directly from the external control system without the use of elastomeric seals. The base is symmetric about its air logic porting. One may note that externally controlled systems theoretically produce no contaminates that could be received into a system. Nevertheless, the pump in accordance with the invention is provided with rapid discharge of all controlling air overboard.
The air logic system is isolated, on the one hand, from the pump, on the other hand, the air logic and air connection system is easily removable and serviceable. Moreover, a clamping block may be inserted laterally into the base, to be locked against the base, maintaining the pump in position. The logic and connection system are easily serviceable in such a package, especially when provided with quick-release capability. Likewise, fluid systems need not be opened in order to conduct air system repairs or service. Since the material in the lines and the pump chambers for liquid is ultra pure, elimination of any possible contact of elastomers, metals, or the like.
A spool valve actuated by a pilot valve detecting the end of a stroke of a diaphragm may be implemented to control the speed and the return of a piston driving or being driven by a diaphragm. However, spool valves may be somewhat treacherous. Spool valves typically receive a signal from one line, and they try to equilibrate that signal at some point. For example, at the end of a stroke, the pilot valve cannot move, and air ported through the pilot valve accumulates in a location. As the pressure in a specific location rises, it may act in an axial direction (transversely with respect to an axis of the driving shaft on the pistons) to shift the position of the spool or shuttle. Stabilizing shifting pressure at a specific location has traditionally been difficult.
A detent or bias mechanism may be implemented in accordance with the invention. Previous diaphragms have typically been frameloaded. For example, in flange-mounted diaphragms, a widely varying range of pressures results in shifting a spool or shuttle. Overcoming friction and the like may provide unreliable forces. In an apparatus and method in accordance with the invention, a snap disk is positioned to a collar and shaft of a spool. A disk is maintained in a cavity restricting the diameter thereof. Nevertheless, longitudinally, with respect to the shuttle or spool, the detent is free to move.
The detent is free to move axially, with respect to the spool or shuttle within a gap freely. However, the detent must break over a center in order to change position between a first biased position deflected in a first direction and a second biased position deflected in a second opposite direction axially with respect to the spool. Moreover, the detent may be made of a particularly stiff material rather than a softer, more flexible elastomeric material. The effect of the more rigid, stiff, radially-constrained, axially-free bias detent is to provide a strict, digital motion of the spool at a narrowly repeatable pressure change.
In keeping with a virtually absolute prohibition against a metallic or otherwise reactive materials in the air path and the liquid path of a pump in accordance with the invention, a rapid exhaust valve is provided. Again, rather than common elastomeric materials, a thin, comparatively rigid, stiff film is provided. A disk of the film may be on the order of less than 0.010 inches in thickness. The dump valve or quick exhaust valve is included to divert rather than return controlled air.
For example, a circulating air control is returned to a prime mover. However, external control systems use ambient air, that is discharged after one use. Thus, a plastic disk is provided that deflects to permit passage of air around it""s exterior perimeter and yet to close down against a port at near the center thereof and on the opposite side thereof in response to an airflow in the opposite direction. Thus, a very rapid dump around the exterior parameter of the disk may be conducted, yet no back flow into the lines can occur at any significant rate or total amount.
In one embodiment, a chamber holds the disk. The disk is supported on a grid on one side with fluted walls providing a standoff distance between the outer most radius of the disk and the outer most radius of the containing chamber. Accordingly, air may pass around the disk. The disk is mounted to press against a face of a port occupying an area very near the center of the disk on one side. During venting, air may pass out of the port against the disk, deflecting the disk and passing around the outermost circumference of the disk. By contrast, any pressure of air against the disk from an opposite side nearly forces the entire disk back against the port, sealing the port off against backflow.
A leak detection scheme may rely on fiber optics. In one embodiment, the leak detectors may include a body containing fiber optic lines disposed at an angle calculated to produce reflection of a beam from one fiber optic line to a receiving, second, fiber optic line, only in the presence of liquids. The difference in refractive indices of air and liquids common to processing in the semiconductor industry is sufficient to detect the presence of liquids in the air chamber actuating the piston.
In one embodiment, the fiber optic lines may be sealed against liquids for direct contact with the chamber of the pump. In another embodiment, a separate window may be provided having a very thin thickness, and formed of a material that is likewise non-metallic, high purity, non-electrical, nonreactive, and sealed. In such an embodiment, an acrylic fiber may be used. Acrylic fibers will absorb more deflection during handling.
By contrast, fiber optics may tend to break when mishandled, such as by being bent on too tight a radius. It is important to protect operators from being sprayed by exhaust or by controller exhaust when an external controller is used to operate a pump in accordance with the invention. In such an environment, a chamber filled with fluid, may be evacuated by the continuing operation of an external controller, unresponsive to the leak. In one presently preferred embodiment, a window completely seals the chamber from the leak detector, as an acrylic, fiber optic line may be used.
The double-line design is superior to prior art systems and other technologies wherein fiber optic lines are laid side-by-side in order to cooperatively send and receive a beam. The difficulty with such embodiments often includes an inability to define a digital location at which reflected light intensity indicates either a liquid is present or that an end of stroke of the pump has been reached. By using off-axis orientations between the sending and receiving fibers, the index of refraction or the presence of a film layer creates a dramatic, even digital demarcation between a desired condition and an undesired condition.
In one embodiment, a leak detector may be located near an outer circumference of a chamber in which a diaphragm is operating. In such an embodiment, another leak detector may be positioned centrally or elsewhere within an air chamber in order to identify an end of a stroke by the pump. Accordingly, an external controller may use a fiber optic detector for the end of the stroke of the diaphragm of the pump.
For example, as in parallel lines that become retroreflective, a pre-determined angle may be established between two, separate, cooperative fiber optic lines. The difficulty of establishing a value or trigger lever for the reflected light from a sending fiber to a receiving fiber is eliminated by the construction in accordance with the invention. Rather, the range of distance within which a diaphragm positioned to reflect light from the sending fiber to the receiving fiber may be adjusted within a very narrow range. The narrowness of the range is sufficiently precise to be effective for operational functionality of the pump.
The signal corresponding to the reflection of light quickly decays to a minimal value far from that corresponding to a trigger position. Whenever the diaphragm moves away from a specific location designed for the sensor. Thus, a detector in accordance with the invention provides a digital signal rather than an analog signal, for all practical purposes with respect to detecting the end of stroke for controlling the operation of the pump.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.